Use of springs and spring assemblies for effecting throttle valve operation is well known in the art. Reference may be made to Blanchard et al. U.S. Pat. No. 4,582,653, which is incorporated herein by reference, for a more detailed disclosure of a typical throttle body equipped with a spring assembly for returning a throttle valve toward a closed position.
FIGS. 1-3 illustrate a prior art single torsion spring assembly 10. The spring assembly 10 is described in detail in Pavlin U.S. Pat. No. 5,368,283 which is incorporated herein by reference. The spring 10 is referred to herein as a single torsion spring because it is coiled from a single strand of music wire. Reference is also made to Paggeot U.S. Pat. No. 4,828,235 which describes a similar single torsion spring, and which is also incorporated herein by reference.
The spring assembly 10 is shown in FIGS. 1-2 in conjunction with a throttle body 11 of an automobile internal combustion engine. The throttle body 11 includes a lever 12 supported to rotate about the axis of a shaft 13 (FIG. 2). Rotation of the lever 12 in one direction effects opening of the throttle valve (not shown) of the throttle body 11, while reverse rotation of the lever 12 by the spring assembly 10 effects closing of the throttle valve.
The spring assembly 10 includes a coiled torsion spring 15 having two coils 15A adjacent each end of the spring and a pair of end bushings 16 and 17 (FIG. 3). The torsion spring 15 is wound helically from round music wire and is formed with the end coils 15A being of a reduced diameter. The end coils 15A of the single torsion spring are of equivalent diameter, albeit reduced from the diameter of intermediate coils. Tangs 24 and 25 extend radially from the coils. One tang is parallel to a longitudinal axis of the spring.
A dual torsion spring, that is a spring comprising two coiled strands, may be produced by coiling the two strands about a coiling shaft (or simply shaft). The dual torsion spring is then slid off of the shaft. Such a shaft wound dual torsion spring is not capable of having two reduced reduce end coils, one on either side of the intermediate coils. Further, one reduced end coil is difficult to achieve via a shaft wound method. These limitations are a result of the fact that a spring wound as such on a shaft cannot be slid off of the shaft after it is formed without deforming it.
Recently dual torsion springs having reduced end coils, wherein the end coils are of equivalent diameters, have become known in the art. FIGS. 4-7 illustrate such a prior art dual torsion spring 30. The dual torsion spring 30 has a first end coil 32 and a second end coil 34 separated by intermediate coils 36. The first end coil 32 has a diameter 38 and the second end coil 34 has a diameter 40 of the same size. Both end coil diameters are reduced in size as compared to a diameter 42 of the intermediate coils 36.
The dual wound torsion springs shown in FIGS. 4-7 have been produced utilizing what may be referred to as single-wound technology. Each strand is formed into a coil and then, through post-wind operation, the strands are merged into a dual torsion spring. Heretofore, known manufacturing techniques required each end coil to be of equal diameters. This had certain disadvantages, particularly relevant to shafts of throttles, wherein the shafts had to be over built (or over molded) at one end to accommodate the diameter of an end coil. With reference to FIGS. 1 and 2, this would generally require shaft 13 to be over built near lever 12.
Embodiments of the present invention overcome these and other problems.